Pressure-sensitive adhesive tape which is wound upon itself in roll form has a low-adhesion backsize coating to permit the tape to be unwound without delaminating. If the tape is not wound upon itself, its adhesive is customarily protected by a disposable web which likewise has a low-adhesion coating. Any such low-adhesion coating must both adhere strongly to its underlying substrate and be sufficiently cohesive not to contaminate the adhesive, i.e., not to interfere unduly with its adhesiveness. Low-adhesion backsize coatings are disclosed in U.S. Pat. Nos. 3,318,852; 3,536,749; 4,057,596 and 4,216,252.
Certain pressure-sensitive adhesives are so aggressively tacky that tapes require undesirably high peel forces to be removed from known low-adhesion backsize coatings, especially after prolonged storage. Such tapes may carry away and thus be contaminated by appreciable amounts of the low-adhesion material. It is believed that no release coating of the prior art is fully effective for use with aggressively tacky poly(dimethylsiloxane) pressure-sensitive adhesives.
The need for improved low-adhesion coatings is especially acute for pressure-sensitive adhesive tapes having porous backings such as breathable medical tapes. When such tapes are wound upon themselves into roll form, the pressure-sensitive adhesive may gradually flow into the pores of the backing and thus create a mechanical bond that may cause the adhesive layer to split upon unwinding unless the low-adhesion backsize coating is exceedingly effective. For some such tapes it has been necessary to employ a nonporous, disposable, low-adhesion web, the cost of which could have been avoided if a better low-adhesion backsize coating were available.
Pressure-sensitive adhesive transfer tapes which are marketed in roll form usually have a carrier web having low-adhesion coatings on both surfaces, one of which provides a lower unwinding force so that the adhesive layer remains on the carrier web during unwinding. If the pressure-sensitive adhesive is highly aggressive, the low-adhesion coating which is to provide the higher unwinding force must accomplish the aforementioned objectives, and the low-adhesion coating which is to provide the lower unwinding force must be even more effective.
Coatings comparable to low-adhesion backsize coatings have other uses, e.g., nonstick coatings for cooking utensils, ice-releasing coatings for aircraft, and lubricative coatings for magnetic recording media. Such low-adhesion coatings are sometimes called "release coatings", a term which also encompasses release agents for molds, which may be effective only by falling cohesively. Lubricants usually function by cohesive failure. To distinguish release coatings which are designed to fail cohesively from those which are designed to resist cohesive failure, the latter are here called "liners[ and, more specifically, "low surface energy liners" because low surface energy is important to their effectiveness.